The shipment of temperature-sensitive goods is extremely difficult when the shipping container itself is not independently temperature-controlled; ie., does not have an independent power source for maintaining interior temperatures within close parameters. Of course, if it is merely desired to maintain an object to be shipped at a nominally cooled temperature—relative to the ambient exterior temperature—a common practice is to pack a shipping container with ice, and hope that the ice will remain in a frozen state during transit so that the object shipped will arrive at its destination still cooled below ambient temperature. This can be an adequate technique for shipping objects where temperature control is not critical. However, even in this case, the temperatures at different points inside the shipping container will vary widely, with parts of the interior of the container becoming quite cool, and other parts of the interior warming to various degrees, depending on time and the distance and spatial relationship of the shipped object to the cooling ice which remains in the container.
Goods such as medical supplies, blood, and vaccines are often extremely temperature sensitive and need to be maintained within a given temperature range. Transport is particularly challenging. Such temperature sensitive goods are shipped to a variety of destinations where the ambient outside temperature varies from extreme cold to extreme heat.